Continuous process for rapidly bleaching woven cotton fabric



Fwaso ea zuzsmssa RVQQWI 1960 H. L. POTTER ET AL 2,960,383

CONTINUOUS PROCESS FOR RAPIDLY BLEACHING WOVEN COTTON FABRIC Filed July 25, 1958 OOTTOII FABRIC HO AT 200-2 20F AQUEOUS SOLUTION:

I $COUR 2.5-O% SODIUM HYOROXIDE FOR Z-I 0 MINUTES O.5-I% TETRASOOIUIA PYROPHOSPI'IATE RINSE WATER AOUEOUS SOLUTION! -SOUR 57, AOETIO AOIO OPTIONAL STEPS RIIISE IATER AQUEOUS SOLUTION IIOLO AT ZOO-ZIZ'F. 070.6% SOOIUIA IIYOROXIOE FOR 2-IO MINUTES l-S'l SODIUM SILIOATE O.5'l.2% HYDROGEN PEROXIOE RmsEI WATER BLEAOHEO FAORIO United States Patent CONTINUOUS PROCESS FOR RAPIDLY BLEACH- ]NG WOVEN COTTON FABRIC Howard L. Potter and Hugh D. Terhune, Wilmington,

Del., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed July 25, 1958, Ser. No. 750,869-

4 Claims. (Cl. 8-111) This invention relates to a continuous process for rapidly bleaching woven cotton fabric. More particularly, this invention relates to a process in which there is initially used a high caustic, NaOH, scouring bath to treat fabric followed by a treatment in a bath containing a relatively high concentration of H 0 wherein the saturated fabric after each treatment is held for short periods of time at temperatures of 200 F. or more.

Prior art bleaching processes in general include steps for scouring fabric with a caustic solution before treating the fabric with a bleaching solution. Conventional scouring baths frequently incorporate relatively high concentrations of caustic for initially purifying the fabric and bleaching baths that have moderate peroxide concentrations. Other known processes employ scouring baths of comparatively low caustic concentration followed by treatment with bleaching baths containing a high concentration of peroxide. These processes usually require from one to several hours to bleach woven cotton fabrics.

Fabric treated by the present process may be bleached to a full white (about 88-90% Hunter) in considerably less time than one hour. However, the present invention is limited to certain concentrations of caustic in the scour bath as well as certain concentrations of H 0 in the bleaching bath. In addition, the drastic combination of high amounts of caustic and H 0 in the scouring and bleaching solutions, respectively, require that the fabric remain saturated for at least 2 minutes with each solution but not longer than 10 minutes and that the temperature of the saturated fabric in each instance be maintained at 200-212 F. A further limitation is that the fabric must be rinsed after it has remained saturated for 2-10 minutes with each solution.

The present process does not require the use of the heavy equipment usually employed in prior art methods, since fabric is completely processed in a fraction of the time normally necessary. For instance, large J-boxes designed to store two or more tons of saturated cloth for comparatively long periods of time are not needed for cloth treated according to the present invention, since the processing time is greatly reduced.

It is an object of the present invention to provide a process that will efiectively bleach woven cotton fabric in a relatively short period of time.

It is another object of the present invention to provide a process that will effectively bleach woven cotton fabric using an unique combination of conditions under which the fabric is treated with a high caustic scouring bath and a high H 0 bleaching bath without reducing fabric strength.

The above and other objects are accomplished on all weights of woven fabrics including heavy fabrics (1.5 yd./lb. and heavier) even when these fabrics have not been enzyme desized. According to the present invention, woven cotton fabric is first saturated by immersion in an aqueous bath containing by weight about 2.56% of caustic and 0.5-1% of a molecularly dehydrated salt "ice of phosphoric acid to passivate extraneous material found on the fabric and sequester impurities. These dehydrated salts embrace the preferred tetrasodium pyrophosphate or, alternately, equivalent salts such as sodium hexametaphosphate or sodium tripolyphosphate. The use of conventional wetting agents such as Duponol ME (sodium alkyl sulfate) in the scouring bath may be advantageously used in conventional amounts (about 0.2% by weight), although a wetting agent is not essential. Other wetting agents include Alkanol WXN (sodium hydrocarbon sulfonate), Triton X- (alkoxylated aryl polyether alcohol) and the like.

Those fabrics that have not been desized often require 46% caustic in order to substantially remove all of the starch. Below 2% caustic results in insufficient purification and above 6% caustic may damage cotton fabric, since it is to be further treated with a relatively high concentration of H 0 in the second bath.

After the fabric is saturated with the above solution, it is held for 210 minutes at a temperature of 200212 F., and, more preferably, for 58 minutes at 205-2l2 F.

The fabric is next subjected to a water rinse to remove substantially all of the caustic. Before the fabric is treated with the bleaching solution, it may be immersed in an aqueous 0.51.5% acetic acid solution. This latter step, commonly referred to as a sour may be omitted if desired. Souring the fabric slightly increases the degree of brightness as determined with a Hunter Multipurpose Reflectometer. It will be understood, however, that treatment with a sour bath is optional and may be omitted if desired. If a sour is used, however, it should be followed by a water rinse before the cloth is further processed.

The fabric is next immersed in a bleaching bath containing by weight 0-0.6% caustic, 1-3% silicate (the 42 B. sodium silicate normally used in the textile bleaching trade) and 0.5-1.2% H 0 The use of small amounts of caustic in the formula is necessary for best results in the bleaching bath. The preferred caustic concentration is about 0.3%, although acceptable results can be obtained when concentrations within the range of 0 0.6% are employed.

The amount of H 0 may be varied between 05-12% and conventional sources of this amount of H 0 such as Albone 35% H 0 (16.4% by Weight of active oxygen) are suitable. Because of the drastic caustic treatment in the scouring bath, the use of more than 1.2% H 0 is not recommended, since an excess may damage the fabric. Less than 0.5% H 0 is inadequate to effectively bleach the fabric.

At least 1% of silicate must be used to stabilize the H 0 more than 3% of silicate may be used, although little advantage will obtain.

Fabric saturated with the bleaching solution is then retained for 2l0 minutes at 200212 F. and preferably 5-8 minutes at 205-212 F. The fabric may be subjected to steam during the 210 minute period or the fabric may be heated and stored at that temperature without further heating. After this period and before the fabric is dried, it should be rinsed substantially free of the bleaching solution.

-It is to be noted that the periods of time during which the fabric is held at ZOO-212 F. for 2l0 minutes follow steps during which the fabric is immersed or otherwise saturated with treating solutions. These solutions as well as the rinsing bath and the sour bath, if used, may advantageously be heated to above 100 F. in order to preserve heat in the fabric being processed. The bleaching solution, however, should not be heated above F. or some of the H 0 will be destroyed.

The following examples will illustrate various conditions under which the process may be carried out.

3 The first five samples of desized heavy gray cotton twill (2 yd./lb.) were saturated with an aqueous scouring solution containing 3% NaOH, 0.5% TSPP, tetrasodium pyrophosphate, and 0.2% Duponol ME. After 4 perature of said fabric at ZOO-212 F. for 2-10 minutes, rinsing said fabric, saturating said fabric with an aqueous bleaching solution containing by weight 0.6% so dium hydroxide, 1-3% sodium silicate and 0.5-1.2%

a short storage period, the fabrics were rinsed and satu- 5 H 0 storing said fabric for 2-10 minutes at 200-212" rated with an aqueous bleaching solution containing F. and thereafter rinsing said fabric. 1.05% H 0 and 1.5% silicate. 2. The process of claim 1 wherein the salt of phos- Four samples of heavy gray cotton twill (2 yd./lb.) phoric acid is tetrasodium pyrophosphate. that had not been desized were first saturated with a 3. In a continuous process for rapidly bleaching woven scouring solution containing 5% NaOH, 1% TSPP and cotton fabric which comprises saturating said fabric with 0.2% Duponol ME. After the storage period and hot an aqueous scouring solution containing by weight 2.5- water rinse the sample 6 fabric was saturated with an 6% sodium hydroxide, and 0.5-1% of a molecularly aqueous bleaching solution similar to that used on the dehydrated salt of phosphoric acid, maintaining the temfirst five samples. Fabric samples 7-9, inclusive, were perature of said fabric at 200-212 F. for 2-10 minutes, all saturated with an aqueous sour 1% acetic acid) rinsing said fabric before and after the fabric has been before treatment with the bleaching solution. The persaturated with a sour solution containing by weight cent whiteness obtained using the process was entirely 0.51.5% acetic acid, rinsing said fabric, saturating said unexpected in view of the short time storage periods used fabric with an aqueous bleaching solution containing by after the scour and bleach stages. weight 0-0.6% sodium hydroxide, 1-3% sodium silicate Table I ENZYME DESIZED Bleach Sample Percent Time, No. Scour Sour itemin.

Percent ness NaOH 3% NaOH 105,7 H 0 0 89.0 8 0.5 TSPP! N 1 0.2 90.1 8 gggqugfip ln ME one {1.5% Silicate OA 89.4 8 v a 1.057 H o 0.1 86.8 5 {8:23; l igig zr None {l.5% Si1i cai.e 0.3 87.7 5

NO ENZYME lDESIZE 5 N on 6 {1% T PP }Nm1e 0.3 87.4 s i I O E 0 2 90 s A A d v 0.4 89.7 s iili 7 f l i iponol 1% mm m {15%S1hcate Each sample was rinsed thoroughly in hot (140 F.) tap water following scour and bleach saturation treatl trasodium pyrophosphate.

'- Time is for each scour and bleach stage at 2052l2 F.

Fabrics treated according to the foregoing are efiectively bleached full white with little or no loss in strength. This result could not be anticipated because the short time employed for scouring would be expected to insufliciently purify the fabric for bleaching. Expectation was that considerably more than 0.6% caustic would be necessary in the bleaching bath to effectively purify the fabric and the process would not be operative since higher concentrations of caustic would considerably weaken the fabric.

The essential features of the process, including the steps of successively saturating fabric with high caustichigh H 0 for short periods of time, most unexpectedly are capable of imparting high absorbtivity to even heavy twill. Such fabrics are effectively bleached by the process and are ready for dyeing.

The embodiments of the invention in which an exclusive propery or privilege is claimed are defined as follows:

1. In a continuous process for rapidly bleaching Woven cotton fabric which comprises saturating said fabric with an aqueous scouring solution containing by weight 2.5- 6% sodium hydroxide, and 0.51% of a molecularly dehydrated salt of phosphoric acid, maintaining the temand 0.5-1.2% H 0 storing said fabric for 2-10 minutes at ZOO-212 F. and thereafter rinsing said fabric.

4. In a continuous process for rapidly bleaching woven cotton fabric which comprises saturating said fabric with an "aqueous scouring solution containing by weight 3-5 sodium hydroxide, and 0.51% of a molecularly dehydrated salt of phosphoric acid, maintaining thetemperature of said fabric at 205212 F. for 5-8 minutes, rinsing said fabric, saturating said fabric with an aqueous bleaching solution containing by weight 00.6% sodium hydroxide, 13% sodium silicate and 0.5-1.2% H 0 storing said fabric for 5-8 minutes at 205-212 F. and thereafter rinsing said fabric.

References Cited in the file of this patent UNITED STATES PATENTS 2,740,689 Easton et al Apr. 3, 1956 2,858,183 Potter Oct. 28, 1958 FOREIGN PATENTS 21,631/35 Australia Mar. 4, 1936 490,382 Great Britain Aug. 15, 1938 

1. IN A CONTINUOUS PROCESS FOR RAPIDLY BLEACHING WOVEN COTTON FABRIC WHICH COMPRISES SATURATING SAID FABRIC WITH AN AQUEOUS SCOURING SOLUTION CONTAINING BY WEIGHT 2.56% SODIUM HYDROXIDE, AND 0.5-1% OF A MOLECULARLY DEHYDRATED SALT OF PHOSPHORIC ACID,MAINTAINING THE TEMPERATURE OF SAID FABRIC AT 200-212*F. FOR 2-10 MINUTES, RINSING SAID FABRIC, SATURATING SAID FABRIC WITH AN AQUEOUS BLEACHING SOLUTION CONTAINING BY WEIGHT 0-0.6% SODIUM HYDROXIDE, 1-3% SODIUM SILICATE AND 0.5-1.2% H2O2, STORING SAID FABRIC FOR 2-10 MINUTES AT 200-212* F. AND THEREAFTER RINSING SAID FABRIC. 